A bicycle speed change assembly for sports type bicycles is commonly mounted on a bicycle frame member such as the down tube or the top tube. Therefore, the rider must unhand the handlebar to perform a speed change operation.
As a result, it is impossible to immediately perform a braking operation during the speed change operation. In addition, the rider has to assume a single hand steering, which leads to unstable handlebar operation and poor safety.
On the other hand the speed change operation is required, in general, when road conditions change, for example, from a flat road to a slope, or vice versa. In such occasions the bicycle becomes unstable and the brake operation is often needed.
In an attempt to solve this problem the Japanese Utility Model Laid-open 58-46693 discloses a grip rotating type speed change operation assembly, wherein a cylindrical operation member is fitted around each of the left and right grip portion of the handlebar, and these cylindrical operation members are rotated to pull or pay out the speed control cable.
In this grip rotating type speed change operation assembly, it becomes possible to perform a speed change operation without unhanding the handlebar grip portion, resulting in remarkable improvement in riding safety during speed change operation.
In off-road riding on a mountain bike for example, it is sometimes necessary to perform a speed change operation during a braking operation.
In such a case, with the conventional grip rotating type speed change operation assembly, the brake must be operated while the cylindrical operation member gripped by the hand and fingers must be rotated at the same time. However, when the speed change operation is required through a plurality of speed steps, the amount of rotation required for the speed change operation member becomes large, and therefore, the hand and finger must be repositioned. Thus, it is very difficult to perform a speed change operation in optimum response to different riding situations while keeping the fingers engaged with the brake lever.
In addition the speed change operation is performed in various ways in response to the changing running situation; sometimes the speed change operation is made in a stepped manner, or some other times the speed change operation is made all the way through several speed steps as mentioned earlier. It is too demanding to perform the speed change operation in many different ways using only one operation member.